Plenty of activists, even those with radical opinions, take that approach. They have a long term goal in mind, but to get to that goal they try to make incremental changes with the power they have.

Hermione got involved in house-elf welfare as an adult and was successful. I am not sure where that is covered, I think maybe Cursed Child? I don’t know much about what happens after the series is over, so I can’t speak to that in detail.

The fatphobia is real, but I’ve never bought the bit about the books being against Hermione’s anti-slavery stance (I assume that’s what you mean by a woman who speaks up as well). My interpretation was that Hermione was always assumed to be in the right because slavery is almost universally condemned in modern society. But she’s standing up against a system where even one of her two closest friends has been indoctrinated into it. Standing up to “others” is hard, but standing up to peer pressure is harder.

That said, the depiction of chattel slavery is of course inaccurate. Slave revolts were common, whereas the house elves want to be subservient to humans. I guess that could be marked up to house elves being a distinct species that may have been manipulated to be subservient, but that’s never explained.